The present invention relates to ultrahigh purity copper having a purity of 8N (99.999999 wt %) or higher and the manufacturing method thereof in which a single electrolytic vessel is used to perform the dissolution and extraction of raw material copper.
High purity copper is characterized in that the recrystallization temperature is low and it is soft, there is hardly any brittleness in the intermediate temperature range and it has favorable workability, the electrical resistance is small at ultracold temperatures and it has high thermal conductivity, and also characterized in that it is subject to great influence from improved characteristics due to addition of infinitesimal quantity of elements or impurity contamination.
High purity copper is widely used as various electronic component materials and semiconductor device materials by utilizing the foregoing characteristics. In particular, when using a sputtering target to form a high purity copper thin film, stability of the deposition characteristics and deposition conditions depend largely on the purity of the target, and the high purification of target materials is strongly demanded.
As conventional technology, there are disclosed ultrahigh purity copper having a purity of 99.99999% (7N) or higher in which the elongation at room temperature is 30% or higher and the Vickers hardness is 42 or less (for instance, refer to Japanese Patent Laid-Open Publication No. H2-185990), a manufacturing method of high RRR (residual resistance ratio) copper material in which a copper material having a purity of 99.999% or higher is heated at 650 to 800° C. in an inert gas atmosphere for at least 30 minutes or longer (for instance, refer to Japanese Patent Laid-Open Publication No. H4-224662), and a method of evaluating the purity of copper by measuring the residual resistance ratio of copper having a purity of 99.999 wt % or higher and creating in advance an analytical curve between such residual resistance ratio and purity, measuring the residual resistance ratio of copper subject to purity evaluation, and measuring the purity of copper using the analytical curve based on the measurement results (for instance, refer to Japanese Patent Laid-Open Publication No. H3-20656).
Further disclosed are a superconducting copper material formed from high purity copper containing silver in an amount of 1 ppm or less and sulfur in an amount of 0.5 ppm or less (for instance, refer to Japanese Patent Laid-Open Publication No. S64-56399), and a manufacturing method of monocrystal copper in which high purity copper having a purity of 6N (99.9999%) or higher containing Ag in the range of 2 to 50 ppm is. placed in. a mold and extracted at a casting speed of 50 mm/minute or slower (for instance, refer to Japanese Patent Laid-Open Publication No. H5-309448).